Sensor arrays and methods for making same

ABSTRACT

A system includes a sensor including a sensor pad and includes a well wall structure defining a well operatively connected to the sensor pad. The sensor pad is associated with a lower surface of the well. The well wall structure defines an upper surface and a wall surface extending between the upper surface and the lower surface. The upper surface is defined by an upper buffer material having an intrinsic buffer capacity of at least 2×10 17  groups/m 2 . The wall surface is defined by a wall material having an intrinsic buffer capacity of not greater than 1.7×10 17  groups/m 2 .

FIELD OF THE DISCLOSURE

This disclosure, in general, relates to sensor arrays and methods formaking same.

BACKGROUND

Electronic sensor arrays are finding increased use for detectinganalytes in fluids, such as gases or liquids. In particular, arrays ofsensors based on field effect transistors are finding use in detectingionic components, such as various cations, anions or pH. Such sensorsare often referred to as ion-sensitive field effect transistors orISFETs.

Recently, such sensor arrays have found use in sequencingpolynucleotides. Nucleotide addition results in the release of ionicspecies that influence the pH in a local environment. Sensors of thesensor arrays are used to detect changes in pH in the local environmentresulting from the nucleotide addition. However, the pH of the localenvironment can be influenced by adjacent environments, referred to ascrosstalk, and can be influenced by the interaction of various materialswith hydrogen ions, leading to lower accuracy and less sensitivity tothe changes caused by nucleotide addition.

As such, an improved sensor array would be desirable.

SUMMARY

In a first aspect, a system includes a sensor including a sensor pad anda well wall structure defining a well operatively connected to thesensor pad. The sensor pad is associated with a lower surface of thewell. The well wall structure defines an upper surface and a wallsurface extending between the upper surface and the lower surface. Theupper surface is defined by an upper buffer material having an intrinsicbuffer capacity of at least 2×10¹⁷ groups/m². The wall surface isdefined by a wall material having an intrinsic buffer capacity of notgreater than 1.7×10¹⁷ groups/m².

In a second aspect, a method of forming a sensor system includes forminga structural layer over a sensor device. The sensor device includes asensor pad. The structural layer includes a structural material havingan intrinsic buffer capacity of not greater than 1.7×10¹⁷ groups/m². Themethod further includes forming a buffer layer over the structurallayer. The buffer layer includes a buffer material having an intrinsicbuffer capacity of at least 2×10¹⁷ groups/m². The method also includesetching the buffer layer and the structural layer to define a welloperatively connected to the sensor pad.

In a third aspect, a method of sequencing a polynucleotide includesapplying a particle comprising a plurality of copies of a polynucleotideto a well of a system of the first aspect, exposing the particle to anaqueous solution including a nucleotide, and measuring a response of thedevice to the exposing.

In a fourth aspect, a system includes a sensor device including a sensorpad and a well wall structure defining a well in operative connectionwith the sensor pad. A lower surface of the well is defined over thesensor pad. The well wall structure has an upper surface and a wallsurface extending between the upper surface and the lower surface. Thesystem includes a passivation film disposed over the upper surface, thewall surface and the lower surface and an isolation film disposed overthe passivation film opposite the well wall structure and extendingsubstantially parallel to and at least along a portion of the wallsurface. The passivation layer is exposed at least along a portion ofthe upper surface and at least along a portion of the lower surface.

In a fifth aspect, a method of forming a sensor system includes forminga structural layer over a sensor device, the sensor device including asensor pad and etching the structural layer to define a well operativelyconnected to the sensor pad. A lower surface of the well is defined overthe sensor pad. The structurally layer has an upper surface and a wallsurface extending between the upper surface and the lower surface. Themethod includes forming a passivation film over the structural layer.The passivation film extends along at least a portion of the uppersurface and extends over the wall surface and the lower surface. Themethod further includes forming an isolation film over the passivationfilm and etching the isolation film to expose the passivation film alongat least the portion of the upper surface and at least a portion of thelower surface.

In a sixth aspect, a method of sequencing a polynucleotide includesapplying a particle comprising a plurality of copies of a polynucleotideto a well of a system of the fourth aspect, exposing the particle to anaqueous solution including a nucleotide, and measuring a response of thedevice to the exposing.

In a seventh aspect, a system includes a sensor device including asensor pad and a well wall structure defining a well in operativeconnection with the sensor pad. A lower surface of the well is definedover the sensor pad. The well wall structure has an upper surface, and awall surface extends between the upper surface and the lower surface. Ametal layer is disposed over the well wall structure and extends alongthe upper surface and the wall surface.

In an eighth aspect, a method of forming a sensor system includesforming a structural layer over a sensor device, the sensor deviceincluding a sensor pad, and etching the structural layer to form atrench defining a well post over the sensor pad and a well wallstructure opposite the first structure, the well post extendingvertically higher than the well wall structure. The method furtherincludes depositing a metal layer into the trench and over the well postand the well wall structure, exposing the well post, and etching toremove the well post.

In a ninth aspect, a method of forming a sensor system includes forminga structural layer over a sensor device, the sensor device including asensor pad, etching the structural layer to form a well post over thesensor pad, depositing a metal layer to surround the well post, andetching to remove the well post.

In a tenth aspect, a method of sequencing a polynucleotide includesapplying a particle comprising a plurality of copies of a polynucleotideto a well of a system of the seventh aspect, exposing the particle to anaqueous solution including a nucleotide, and measuring a response of thedevice to the exposing.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure may be better understood, and its numerousfeatures and advantages made apparent to those skilled in the art byreferencing the accompanying drawings.

FIG. 1 includes an illustration of an exemplary system including asensor array.

FIG. 2 includes an illustration of an exemplary sensor and associatedwell.

FIG. 3 includes an illustration of an exemplary well structure.

FIG. 4 includes cross-sectional illustrations of exemplary wellconfigurations.

FIG. 5 through FIG. 33 include illustrations of exemplary work piecesduring exemplary manufacturing processes.

The use of the same reference symbols in different drawings indicatessimilar or identical items.

DETAILED DESCRIPTION

In an exemplary embodiment, a sensor system includes a sensor having asensor pad and a well wall structure defining a well in operativeconnection with the sensor pad. Optionally, a passivation layer isdisposed over the sensor pad and defines a lower surface of the well.The well wall structure defines an upper surface and a wall surfaceextending between the upper surface and the lower surface of the well.In particular, the well wall surface may extend substantiallyvertically, defined as extending in a direction having component that isnormal to a surface defined by the sensor pad. In a particular example,the upper surface is formed of a buffer material having an intrinsicbuffer capacity of at least 2×10¹⁷ groups/m². The wall surface is formedof a wall material having an intrinsic buffer capacity of not greaterthan 1.7×10¹⁷ groups/m². Optionally, the lower surface of the well maybe formed of a material having an intrinsic buffer capacity of at least2×10¹⁷ groups/m². In particular, such a system can reduce the influenceof an adjacent wells on the local environment of the well and canimprove sensitivity of the sensor.

In a particular embodiment, a sequencing system includes a flow cell inwhich a sensory array is disposed, includes communication circuitry inelectronic communication with the sensory array, and includes containersand fluid controls in fluidic communication with the flow cell. In anexample, FIG. 1 illustrates an expanded and cross-sectional view of aflow cell 100 and illustrates a portion of a flow chamber 106. A reagentflow 108 flows across a surface of a microwell array 102, in which thereagent flow 108 flows over the open ends of microwells of the microwellarray 102. The microwell array 102 and a sensor array 105 together mayform an integrated unit forming a lower wall (or floor) of flow cell100. A reference electrode 104 may be fluidly coupled to flow chamber106. Further, a flow cell cover 130 encapsulates flow chamber 106 tocontain reagent flow 108 within a confined region.

FIG. 2 illustrates an expanded view of a microwell 201 and a sensor 214,as illustrated at 110 of FIG. 1. The volume, shape, aspect ratio (suchas base width-to-well depth ratio), and other dimensionalcharacteristics of the microwells may be selected based on the nature ofthe reaction taking place, as well as the reagents, byproducts, orlabeling techniques (if any) that are employed. The sensor 214 can be achemical field-effect transistor (chemFET), more specifically anion-sensitive FET (ISFET), with a floating gate 218 having a sensorplate 220 separated from the microwell interior by a passivation layer216. The sensor 214 can be responsive to (and generate an output signalrelated to) the amount of a charge 224 present on passivation layer 216opposite the sensor plate 220. Changes in the charge 224 can causechanges in a current between a source 221 and a drain 222 of thechemFET. In turn, the chemFET can be used directly to provide acurrent-based output signal or indirectly with additional circuitry toprovide a voltage-based output signal. Reactants, wash solutions, andother reagents may move in and out of the microwells by a diffusionmechanism 240.

In an embodiment, reactions carried out in the microwell 201 can beanalytical reactions to identify or determine characteristics orproperties of an analyte of interest. Such reactions can generatedirectly or indirectly byproducts that affect the amount of chargeadjacent to the sensor plate 220. If such byproducts are produced insmall amounts or rapidly decay or react with other constituents, thenmultiple copies of the same analyte may be analyzed in the microwell 201at the same time in order to increase the output signal generated. In anembodiment, multiple copies of an analyte may be attached to a solidphase support 212, either before or after deposition into the microwell201. The solid phase support 212 may be microparticles, nanoparticles,beads, solid or porous comprising gels, or the like. For simplicity andease of explanation, solid phase support 212 is also referred herein asa particle. For a nucleic acid analyte, multiple, connected copies maybe made by rolling circle amplification (RCA), exponential RCA, or liketechniques, to produce an amplicon without the need of a solid support.

In a particular example, FIG. 3 illustrates a system 300 including awell wall structure 302 defining wells 304. The wells 304 are inoperative connection with sensor pads 306 of sensors. In particular, alower surface 308 of the well 304 is defined over at least a portion ofthe sensor pad 306. The well wall structure 302 defines an upper surface310 and defines a wall surface 312 extending between the upper surface310 and the lower surface 308.

The well wall structure 302 can be formed of one or more layers ofmaterial. In an example, the well wall structure 302 can have athickness extending from the lower surface 308 to the upper surface 310in a range of 0.3 micrometers to 10 micrometers, such as a range of 0.5micrometers to 6 micrometers. The wells 304 can have a characteristicdiameter, defined as the square root of 4 times the cross-sectional area(A) divided by Pi (e.g., sqrt(4*A/π), of not greater than 5 micrometers,such as not greater than 3.5 micrometers, not greater than 2.0micrometers, not greater than 1.6 micrometers, not greater than 1.0micrometers, not greater than 0.8 micrometers or even not greater than0.6 micrometers.

In a particular example, the upper surface 310 is defined by an upperbuffer material having an intrinsic buffer capacity of at least 2×10¹⁷groups/m². Intrinsic buffer capacity is defined as the surface densityof hydroxyl groups on a surface of a material measured at a pH of 7.Such a buffer material is referred to as a high intrinsic buffercapacity material. For example, the upper buffer material can have anintrinsic buffer capacity of at least 4×10¹⁷ groups/m², such as at least8×10¹⁷ groups/m², at least 1×10¹⁸ groups/m², or even at least 2×10¹⁸groups/m². In an example, the upper buffer material has an intrinsicbuffer capacity of not greater than 1×10²¹ groups/m².

In particular, the upper buffer material is a high intrinsic buffercapacity material that can include an inorganic material, such as aceramic material. For example, a ceramic material can include an oxideof aluminum, hafnium, tantalum, zirconium, or any combination thereof.In an example, the ceramic material can include an oxide of tantalum. Inanother example, the ceramic material includes an oxide of zirconium. Ina further example, the upper surface 310 can be coated with a pHbuffering coating. An exemplary pH buffering coating can include afunctional group, such as phosphate, phosphonate, catechol,nitrocatechol, boronate, phenylboronate, imidazole, silanol, anotherpH-sensing group, or a combination thereof.

The wall surface 312 is defined by a wall material having a lowintrinsic buffer capacity, such as not greater than 1.7×10¹⁷ groups/m².For example, the intrinsic buffer capacity of the wall material can benot greater than 1×10¹⁷ groups/m², such as not greater than 5×10¹⁶groups/m², not greater than 2×10¹⁶ groups/m², not greater than 1×10¹⁶groups/m², or even not greater than 5×10¹⁵ groups/m².

In an example, the wall material includes a low intrinsic buffercapacity material that can include an inorganic material, such as aceramic material. An exemplary ceramic material can include a nitride ofsilica, titanium, or a combination thereof. In another example, theceramic material includes an oxide of silicon. In an additional example,the ceramic material can include silicon oxynitride. In a furtherexample, the inorganic material can include a metal. For example, themetal can include aluminum, copper, nickel, titanium, silver, gold,platinum, or a combination thereof. In particular, the metal can includecopper.

Alternatively, the wall material can include an organic material, suchas a polymeric material. An exemplary polymeric material includes apolymer having an aromatic group in its backbone. For example, thepolymer can be a poly(xylylene), such as a poly(p-xylylene), optionallyincluding functionalize p-xylylenes, such as halogenated p-xylylenes. Inanother example, the polymeric material includes a fluoropolymer. Anexemplary fluoropolymer includes polytetrafluoroethylene (PTFE),polyvinylidene fluoride (PVDF), polyvinyl fluoride (PVF), fluorinatedethylene propylene (FEP) copolymer, ethylene chlorotrifluoroethylene(ECTFE) copolymer, a copolymer of tetrafluoroethylene,hexafluoropropylene, and vinylidene fluoride (THV), a copolymer oftetrafluoroethylene and perfluoro methylvinylether (PFA or MFA), afluoropolymer having a fluorinated oxolane in its backbone,perfluoroether, or any combination thereof. In particular, thefluoropolymer can be a fluoropolymer having fluorinated oxolane in itsbackbone, for example, Cytop. Further, the polymer coating can beamorphous, exhibiting little or no crystallinity.

In a further example, the wall material can include a low buffercapacity coating. In particular, the low buffer capacity coating caninclude a silane component. In an embodiment, the silane component canbe R—[(CH2)n]—Si—[X1 X2 X3] where R is an organofunctional group,[(CH2)n] is a hydrocarbon linker (n=1 to 20), Si is a silicon atom, andX1, X2, or X3 comprise one or more independent hydrolysable groups,including alkoxy or halogen groups. In another embodiment, the silanecomponent can be R—[(C2H4O)n]—Si—[X1 X2 X3] where R is anorganofunctional group, [(C2H4O)n] (n=1 to 100) is a polyether linker,Si is a silicon atom, and X1, X2, or X3 comprise one or morehydrolysable groups, including alkoxy or halogen groups. In either ofthe embodiments, organofunctional groups R can include methyl,methylene, phenyl, benzyl, anilino, amino, amide, hydroxyl, aldehyde,alkoxy, halo, mercapto, carboxy, acyl, vinyl, allyl, styryl, epoxy,isocyanato, glycidoxy, acryloxy, or a combination thereof. Examples ofthe silane component can includeN-((6-aminohexyl)aminomethyltriethoxysilane,(mercaptomethyl)methyldiethoxysilane, chloromethyltriethoxysilane,(isocyanatomethyl)methyldimethoxysilane,N-phenylaminomethyltriethoxysilane, triethoxysilylundecanal,11-mercaptoundecyltrimethoxysilane, 10-undecenyltrimethoxysilane,N-(2-aminoethyl)-11-aminoundecyltrimethoxysilane,11-bromoundecyltrimethoxysilane, n-octyltrimethoxysilane,2-[methoxy(polyethyleneoxy)propyl]trimethoxysilane,3-methoxypropyltrimethoxysilane, methoxytriethyleneoxypropyltrisilane,methoxy silane, methoxyethoxyundecyltrichlorosilane,2-[methoxy(polyethyleneoxy)propyl]-trichlorosilane, or a combinationthereof.

The lower surface 308 of the well can be defined by lower buffermaterial disposed over the sensor pad 306. For example, the lower buffermaterial can have an intrinsic buffer capacity of at least 2×10¹⁷groups/m², such as at least 4×10¹⁷ groups/m², at least 8×10¹⁷ groups/m²,at least 1×10¹⁸ groups/m², or even at least 2×10¹⁸ groups/m². In aparticular example, the lower buffer material has an intrinsic buffercapacity of not greater than 1×10²¹ groups/m². In an example, the lowerbuffer material can include an inorganic material, such as a ceramicmaterial. For example, a ceramic material can include an oxide ofaluminum, hafnium, tantalum, zirconium, or any combination thereof. Inparticular, the ceramic material can include an oxide of tantalum. Inanother example, the ceramic material includes an oxide of zirconium. Ina further example, the lower surface 308 can be coated with a pHsensitive coating. Exemplary pH sensitive coatings can include afunctional group, such as phosphate, phosphonate, catechol,nitrocatechol, boronate, phenylboronate, imidazole, silanol, anotherpH-sensing group, or a combination thereof. In a further example, thelower buffer material can be the same as the upper buffer material. Forexample, the lower buffer material and the upper buffer material can beformed as a single layer over the well wall structure 302.Alternatively, the upper buffer material and lower buffer material canbe formed as separate layers and can be different.

In particular, the wall surface 312 extends substantially vertically,defined as extending in a direction having a component that is normal tothe surface defined by the sensor pad. For example, as illustrated inFIG. 4, a well wall 402 can extend vertically, being parallel to anormal component 412 of a surface 414 defined by a sensor pad. Inanother example, the wall surface 404 extends substantially vertically,in an outward direction away from the sensor pad, providing a largeropening to the well than the area of the lower surface of the well. Asillustrated in FIG. 4, the wall surface 404 extends in a directionhaving a vertical component parallel to the normal component 412 of thesurface 414. In an alternative example, a wall surface 406 extendssubstantially vertically in an inward direction, providing an openingarea that is smaller than an area of the lower surface of the well. Thewall surface 406 extends in a direction having a component parallel tothe normal component 412 of the surface 414.

While the surfaces 402, 404, or 406 are illustrated by straight lines,some semiconductor or CMOS manufacturing processes can result instructures having nonlinear shapes. In particular, wall surfaces, suchas wall surface 408 and upper surfaces, such as upper surface 410, canbe arcuate in shape or take various nonlinear forms. While thestructures and devices illustrated herewith are depicted as havinglinear layers, surfaces, or shapes, actual layers, surfaces, or shapesresulting from semiconductor processing may differ to some degree,possibly including nonlinear and arcuate variations of the illustratedembodiment.

Returning to FIG. 3, the well wall structure 302 and the surfaces 310,312, and 308 can be defined by one or more materials. Specificembodiments are presented below that identify specific material layers.However, it is understood that various materials described above can besubstituted for the identified material layers.

In a particular embodiment, a well wall structure includes one or morelayers defining the well wall. Such layers can be formed of materialshaving low intrinsic buffer capacity. In addition, the well wallstructure includes a film defining an upper surface of the well wallstructure, which is formed of a buffer material having a high intrinsicbuffer capacity. Further, a lower surface of the well is defined by apassivation material having high buffer capacity. The passivationmaterial is disposed over a sensor pad. For example, FIG. 9 includes anillustration of an exemplary well wall structure 828 that defines a well822 over a passivation layer 610 and a sensor pad 608. The passivationlayer 610 is exposed to form a lower surface 930 of the well 822. Thewell wall structure 828 defines a wall surface 824 extending between anupper surface 826 and the lower surface 930. The well wall structure 828includes one or more layers of low intrinsic buffer capacity materialthat define the wall surface 824. An additional film 720 defines theupper surface 826 and is formed of a high intrinsic buffer capacitymaterial. In an example, a structure such as that illustrated in FIG. 9can be formed by a process such as a process illustrated in FIGS. 5-9.

As illustrated in FIG. 5, a conductive layer 504 is deposited over aCMOS structure 502. The CMOS structure 502 can include a sensorstructure to be operatively coupled to a sensory pad. In addition, oneor more passivation layers 506 or 508 can be deposited over theconductive layer 504. In an example, the conductive layer 504 is formedby a metal deposition technique, such as atomic layer deposition,sputtering, e-beam evaporation, electrochemical deposition, or acombination thereof. The passivation layers 506 or 508 can be depositedover the conductive layer 504 using atomic layer deposition or othertechniques. In particular, the passivation layers 506 or 508 can includean oxide of aluminum, hafnium, tantalum, zirconium, or a combinationthereof. In a particular example, the passivation layer 506 includes anoxide of tantalum and the passivation layer 508 includes an oxide ofaluminum.

The layers 504, 506, or 508 can be patterned to expose a surface of theCMOS structure 502 and define stack structures 606. For example, asillustrated in FIG. 6, a stack structure 606 including a conductivesensor pad 608 can overlie the CMOS structure 502. In the illustratedexample, a layer 610 includes tantalum oxide and a layer 612 includesaluminum oxide. Optionally, an aluminum oxide layer (not illustrated)can be disposed between the sensor pad 608 and the layer 610.Alternatively, the layers 610 or 612 can be formed of zirconium oxide.In an example, each of the layers 610 or 612 can have a thickness in arange of 5 nm to 100 nm, such as a range of 10 nm to 70 nm, a range of15 nm to 65 nm, or even a range of 20 nm to 50 nm.

As illustrated in FIG. 7, one or more layers 714, 716, or 718 can bedeposited over the CMOS structure 502 and the sensor pad 608. In anexample, one or more layers of an oxide of silicon, a nitride ofsilicon, or TEOS can be deposited to overlie the stack structure 606. Inthe illustrated example, a layer 714 of silicon oxide is deposited overthe CMOS structure 502. A layer 716 of silicon nitride is deposited overthe layer 714, and a layer 718 of silicon oxide or TEOS is depositedover the layer 714. In addition, a buffer material layer 720 can bedeposited over the layers 714, 716 or 718. The total thickness of theone or more layers 714, 716, 718, or 720 can be in a range of 0.3micrometers to 10 micrometers, such as a range of 0.5 micrometers to 6micrometers.

As illustrated in FIG. 8, the layers 714, 716, 718, or 720 can be etchedto define a well 822 and a well wall structure 828. In an example, thewells 822 can be exposed using a wet patch, a plasma etch, or acombination thereof. In particular, a fluorinated plasma etch processwith endpoint detection can be utilized to form a well that terminatesat the aluminum oxide layer 612. In particular, a fluorinated plasmaetch using fluorinated species, such as trifluoromethane,tetrafluoromethane, nitrogen fluoride, sulfur hexafluoride, or acombination thereof, can be utilized. As a result, an upper surface 826is defined by the buffer material of the layer 720. The wall surface 824is defined by the material of layers 714, 716, or 718, which are formedof low intrinsic buffer capacity materials.

As illustrated in FIG. 9, a wet etch process can be used to remove aportion of the aluminum oxide layer 612 to expose the tantalum oxidelayer 610 and to define a lower surface 930 of the well 822. As such,the lower surface of the well is formed of a high intrinsic buffercapacity material, while the wall surface 824 is formed of a lowintrinsic buffer capacity material, and the upper surface 826 is formedof a high intrinsic buffer capacity material.

In an alternative process, a similar structure can be formed asillustrated in FIGS. 10-15. For example, as illustrated in FIG. 10,sensor pads 1004 can be formed over a CMOS structure 1002. An insulationmaterial layer 1006 can be deposited over the sensor pads 1004. Theinsulation material layer 1006 can be formed of an insulation material,such as silicon dioxide, silicon oxynitride, or a combination thereof.In an example, the insulation material layer 1006 has a thickness in arange of 0.3 micrometers to 1.5 micrometers, such as 0.4 micrometers to1.0 micrometers, or even a range of 0.4 micrometers to 0.7 micrometers.

As illustrated in FIG. 11, the insulation layer 1006 can be patternedusing lithographic method and can be etched to expose the sensor pads1004. As a result, insulation structures 1108 are formed between thesensor pads 1004.

A high intrinsic buffer capacity material can be deposited over thestructures 1108 and the sensor pads 1004. For example, as illustrated inFIG. 12, layers of high intrinsic buffer capacity material, such asaluminum oxide, hafnium oxide, tantalum oxide, zirconium oxide or acombination thereof, can be deposited over the structures 1108 and thesensor pads 1004. In particular, a layer 1210 of tantalum oxide can bedeposited over the structures 1108 and the sensor pads 1004 and a layer1212 of aluminum oxide can be deposited over the layer 1210 of tantalumoxide. Optionally, a layer (not illustrated) of aluminum oxide can bedeposited between the layer 1210 and the structures 1108 or the sensorypads 1004. In a particular example, the layers 1210 or 1212 can have athickness in a range of 5 nm to 100 nm, such as a range of 10 nm to 70nm, a range of 15 nm to 65 nm, or even a range of 20 nm to 50 nm.

As illustrated in FIG. 13, one or more layers 1314, 1316, or 1318 of lowintrinsic buffer capacity material can be deposited over the layers 1210or 1212. For example, one or more layers silicon oxide, silicon nitride,silicon oxynitride, tetraethoxysilane (TEOS) or a combination thereofcan be deposited over the layers 1210 or 1212. Such low intrinsic buffercapacity materials can be deposited using TEOS deposition techniques.Alternatively, chemical vapor deposition can be used to form suchlayers. In a further alternative, one or more of the layers can beformed of a polymer, such as a polyxylylene or a fluoropolymer.

In the illustrated example, a layer 1314 of silicon dioxide is depositedover the layers 1210 and 1212. A layer 1316 of silicon nitride isdeposited over the layer 1314, and a layer 1318 of silicon dioxide isdeposited over the layer 1316. Optionally, a high intrinsic buffercapacity material layer 1320 can be deposited over the layer 1318. Thetotal thickness of the layers 1314, 1316, or 1318 can be in a range of 1μm to 10 μm, such as a range of 2 μm to 7 μm, or even a range of 3 μm to5 μm. The layer 1320 can have a thickness in a range of 5 nm to 100 nm,such as a range of 10 nm to 70 nm, a range of 15 nm to 65 nm, or even arange of 20 nm to 50 nm.

Following patterning, for example, using lithography followed byetching, a well 1422 is opened through layers 1314, 1316, 1318, or 1320,as illustrated in FIG. 14. A wet etch process, plasma etch process, orcombination thereof can be used to open the well 1422. In an example, aplasma etch with etch stop detection can be used. In particular, afluorinated plasma etch using fluorinated species, such astrifluoromethane, tetrafluoromethane, nitrogen fluoride, sulfurhexafluoride, or a combination thereof, can be utilized.

As illustrated in FIG. 15, a wet etch technique can be used to strip thealuminum oxide layer 1212, exposing the tantalum oxide layer 1210 overthe sensor pad 1004. As a result, a similar structure is formed asdescribed in relation to FIG. 9 in which an upper surface 1524 includesa high intrinsic buffer capacity material, a wall surface 1526 is formedof low intrinsic buffer capacity materials, and a lower surface 1528 ofthe well 1422 includes a high intrinsic buffer capacity material.

In an alternative example, a high intrinsic buffer capacity material canbe deposited in a single layer to form an upper surface of the well wallstructure and a lower surface associated with the well. For example, asillustrated in FIG. 16, one or more layers can be deposited over a CMOSstructure 1602 and sensor pads 1604. The CMOS structure 1602 includes aportion of the sensor device operatively coupled to the sensor pad 1604.One or more layers (1606, 1608, or 1610) of low buffer capacity materialcan be deposited over the sensor pads 1604. Exemplary materials includesilicon dioxide, silicon nitride, silicon oxynitride, tetraethoxysilane(TEOS) or a combination thereof. In the illustrated example, a layer1606 of silicon dioxide is deposited over the sensor pads 1604 and theCMOS structure 1602. A layer 1608 of silicon nitride is deposited overthe layer 1606, and a layer 1610 of silicon dioxide is deposited overthe layer 1608. The layers 1606, 1608, or 1610 can be formed usingchemical vapor deposition (CVD), TEOS deposition through plasma enhancedCVD, a hydrolysis method, or a combination thereof. The total thicknessof the layers 1606, 1608, or 1610 can be in a range of 0.3 micrometersto 10 micrometers, such as a range of 0.5 micrometers to 6 micrometers.

As illustrated in FIG. 17, the layers 1606, 1608, or 1610 can bepatterned using lithographic techniques and can be etched to expose thesensor pads 1604, defining wells 1712. For example, etch technique, suchas wet etch, plasma etch techniques, or a combination thereof, can beused to open the well 1712. In a particular example, a fluorinatedplasma etch using fluorinated species, such as trifluoromethane,tetrafluoromethane, nitrogen fluoride, sulfur hexafluoride, or acombination thereof, can be used.

A film 1814 of high intrinsic buffer capacity material can be depositedover the etched layers 1606, 1608, or 1610 and the sensor pad 1604, asillustrated in FIG. 18. For example one or more layers of aluminumoxide, hafnium oxide, tantalum oxide, zirconium oxide, or a combinationthereof can be deposited using atomic layer deposition technique. In aparticular example, a three layer stack including a layer of aluminumoxide over a layer of tantalum oxide over a further layer of aluminumoxide can be deposited to form the film 1814. The film 1814 can have atotal thickness in a range of 20 nm to 500 nm, such as a range of 20 nmto 300 nm, or even a range of 20 nm to 250 nm. In an example in whichmultiple layers are used to form the film 1814, each of the layers canhave a thickness in a range of 10 nm to 100 nm, such as a thickness in arange of 10 nm to 50 nm, or even a range of 10 nm to 30 nm. In aparticular embodiment, a three layer stack including 20 nm layers ofaluminum oxide, tantalum oxide, and a further layer of aluminum oxidecan be deposited using an atomic layer deposition technique.

A further layer of low intrinsic buffer capacity material can bedeposited over the film 1814. For example, a layer 1816 including anoxide of silicon can be deposited over the film 1814. Alternatively, thelayer 1816 can be formed of nitrides of silicon or other low intrinsicbuffer capacity materials. In particular, the layer 1816 has a thicknessin a range of 50 nm to 1 micrometer, such as a range of 50 nm to 500 nm,or even a range of 100 nm to 300 nm.

The silicon dioxide layer can be anisotropic etched to remove portionsof the layer 1816 from the top surface of the well structure and thelower surface of the well, leaving portions of the layer 1816 on thewell wall, as illustrated in FIG. 19. In addition, a wet etch can beused to strip an aluminum oxide layer, leaving an upper surface and alower surface of exposed tantalum oxide. As a result, an upper surface1918 of the well wall structure 1920 and a lower surface 1922 of thewell 1712 include an exposed high intrinsic buffer capacity material,while a wall surface 1924 is defined by a low intrinsic buffer capacityoxide of silicon.

In another example, a well wall surface can be formed of a polymericmaterial, isolating high intrinsic buffer capacity materials from thewell wall surface and limiting exposure of the high intrinsic buffercapacity materials to the upper surface of the well wall structure and alower surface of the well. Returning to FIG. 17, a well 1712 is definedin one or more layers 1606, 1608, or 1610 to expose a sensor pad 1604.As illustrated in FIG. 20, one or more layers of high buffer capacitymaterial can be deposited as a film 2014. For example, the film 2014 caninclude aluminum oxide, hafnium oxide, tantalum oxide, zirconium oxide,or a combination thereof. In a particular example, layers of aluminumoxide and tantalum oxide are deposited using atomic layer deposition. Inthe illustrated example, a layer of aluminum oxide is deposited over alayer of tantalum oxide, which is deposited over a further layer ofaluminum oxide. A layer 2016 of an inorganic material, such as apolymeric material, is deposited over the film 2014. An exemplarypolymeric material includes a polymer having an aromatic group in itsbackbone. For example, the polymer can be a poly(xylylene), such as apoly(p-xylylene), including functionalize p-xylylenes, such ashalogenated p-xylylenes. In another example, the polymeric materialincludes a fluoropolymer. An exemplary fluoropolymer includespolytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF),polyvinyl fluoride (PVF), fluorinated ethylene propylene (FEP)copolymer, ethylene chlorotrifluoroethylene (ECTFE) copolymer, acopolymer of tetrafluoroethylene, hexafluoropropylene, and vinylidenefluoride (THV), a copolymer of tetrafluoroethylene and perfluoromethylvinylether (PFA or MFA), a fluoropolymer having a fluorinatedoxolane in its backbone, perfluoroether, or a combination thereof. Inparticular, the fluoropolymer can be a fluoropolymer having fluorinatedoxolane in its backbone, for example, Cytop.

As illustrated in FIG. 21, the layer 2016 can be anisotropic wet etchedto remove the polymer from an upper surface 2120 of the well wallstructure 2118 and the lower surface 2124 of the well 1712. Thepolymeric material remains on the wall surface 2122 of the wells 1712.While not illustrated, a tantalum oxide layer can be exposed using a wetetch process to remove aluminum oxide. As a result, well wall structure2118 includes an upper surface 2120 of exposed high intrinsic buffercapacity material, and lower surface 2124 of the well 1712 is defined bythe same high intrinsic buffer capacity material. The layer 2016 ofpolymer forms the wall surface 2122 and isolates the well wall surface2122 from the high intrinsic buffer capacity material of the film 2014.

In a further example, the polymeric material can be substituted with aninorganic material, such as a nitride of silicon or titanium. In aparticular material, the inorganic material is an electricallyconductive material. Following from FIG. 17, FIG. 22 illustrates a film2222 formed of one or more layers of high intrinsic buffer capacitymaterial, such as aluminum oxide, hafnium oxide, tantalum oxide,zirconium oxide, or a combination thereof. The film 2222 can be formedas described above with the thicknesses described above. In a particularexample, a three layer stack, including a layer of aluminum oxide over alayer of tantalum oxide, which is disposed over a layer of aluminumoxide, defines the film 2222. A layer 2224 of electrically conductivematerial is deposited over the film 2222. For example, the layer 2224can be formed of a layer of titanium nitride.

As illustrated in FIG. 23, the layer 2224 can be anisotropic wet etchedto remove the electrically conductive film 2224 from a top surface 2328of a well wall structure 2326 and a lower surface 2330 of the well 1712.The electrically conductive layer 2224 remains along a wall surface2332. Further, an aluminum oxide layer of the film 2222 can be removedto expose a tantalum oxide layer on both the upper surface 2328 and thelower surface 2330.

In a further embodiment, the well walls may be formed of a metallicmaterial. In particular, the metal well walls can be formed using aprocess similar to a Damascene or dual-Damascene process. For example,following from FIG. 12, an oxide layer 2414 can be deposited over layers1210 or 1212, as illustrated in FIG. 24. In particular, the layer 2414is formed of a material that can be removed using a technique that willnot damage or erode metallic layers or structures.

As illustrated in FIG. 25, the layer 2414 can be patterned usinglithographic technique and etched to form well posts 2516. Inparticular, the well posts 2516 are disposed over the sensor pads 1004.

A metal layer 2618 can be deposited over the exposed layers 1210 or1212, in addition to the well post 2516, as illustrated in FIG. 26. Forexample, the metal layer 2618 can be deposited using an electroplatingtechnique. Alternatively, the metal layer 2618 can be deposited usingliquid deposition techniques, sputtering, or evaporation techniques. Themetal layer 2618 can be formed of a metal such as aluminum, copper,titanium, nickel, gold, silver, platinum or any combination thereof.

As illustrated in FIG. 27, the metal layer 2618 can be planarized toexpose the well post 2516. For example, a chemical mechanical polishingtechnique can be utilized to planarize the metal layer 2618 and exposethe well posts 2516.

The well posts 2516 can be etched, for example, using a plasma etchtechnique, such as a reactive ion etch, to remove the well post 2516,leaving the metallic layer 2618 to define wells 2820, as illustrated inFIG. 28. While not illustrated, the aluminum oxide layer 1212 can beremoved using a wet etch technique to expose the tantalum oxide layer1210 over the sensor pad 1004.

In an alternative example, ceramic materials can be used to supportmetallic layers that define the well wall. For example, following fromFIG. 24, the layer 2414 can be etched in a pattern. In particular, thelayer 2414 can be patterned using a lithographic technique and etched toform a trench 2918, as illustrated in FIG. 29. A well post 2916 isdefined on an opposite side of the trench 2918 from a well wallstructure 2914. In a particular example, the well post 2916 extends to agreater height over the CMOS structure 1002 than the well wall structure2914.

As illustrated in FIG. 30, a metal layer 3020 can be deposited over thewell wall structure 2914 and the well post 2916 and within the trench2918. For example, the metal layer 3020 be deposited using anelectroplating technique. Alternatively, the metal layer can bedeposited using liquid deposition techniques, sputtering, evaporationtechniques, or a combination thereof. The metal layer 3020 can be formedof a metal such as aluminum, copper, nickel, gold, platinum, silver,titanium, or a combination thereof.

The metal layer 3020 can be planarized using, for example, chemicalmechanical polishing to expose the well posts 2916, leaving a portion ofthe layer 3020 over the well wall structure 2914, as illustrated in FIG.31. The well posts 2916 can be etched, removing the well posts 2916 andleaving wells 3224, as illustrated in FIG. 32. In addition, an aluminumoxide layer 1212 can be removed using a wet etch process to expose atantalum oxide layer 1210 disposed over the sensor pad 1004.

Optionally, an additional planarization process can be used to removethe metal layer 3020 from the upper surface 3322 of the well wallstructure 3320, as illustrated in FIG. 33. As a result, the wall surface3326 is defined by a metallic material, whereas the lower surface 3324of the well 3224 is defined by high intrinsic buffer capacity material.

In each of the above embodiments in which a passivation layer, such asan oxide of tantalum, aluminum, hafnium, or zirconium, is disposed overthe sensor pad and is exposed as part of the lower surface of a well, acoating such as those described above in relation to FIG. 3 can be usedto enhance sensitivity of the system. Further, exposed upper surfaces ofwell wall structures can be enhanced with such coatings. In addition,coatings described above in relation to FIG. 3 that reduce the intrinsicbuffer capacity of a surface can be used on the wall surfaces.

In a first aspect, a system includes a sensor including a sensor pad anda well wall structure defining a well operatively connected to thesensor pad. The sensor pad is associated with a lower surface of thewell. The well wall structure defines an upper surface and a wallsurface extending between the upper surface and the lower surface. Theupper surface is defined by an upper buffer material having an intrinsicbuffer capacity of at least 2×10¹⁷ groups/m². The wall surface isdefined by a wall material having an intrinsic buffer capacity of notgreater than 1.7×10¹⁷ groups/m².

In an example of the first aspect, the upper buffer material has anintrinsic buffer capacity of at least 4×10¹⁷ groups/m². For example, theupper buffer material can have an intrinsic buffer capacity of at least8×10¹⁷ groups/m², such as an intrinsic buffer capacity of at least1×10¹⁸ groups/m², or at least 2×10¹⁸ groups/m². In a particular exampleof the first aspect, the upper buffer material has an intrinsic buffercapacity of not greater than 1×10²¹ groups/m².

In another example of the first aspect or the above examples, the wallmaterial has an intrinsic buffer capacity of not greater than 1×10¹⁷groups/m². For example, the wall material has an intrinsic buffercapacity of not greater than 5×10¹⁶ groups/m², such as an intrinsicbuffer capacity of not greater than 2×10¹⁶ groups/m², not greater than1×10¹⁶ groups/m², or not greater than 5×10¹⁵ groups/m².

In a further example of the first aspect or the above example, the lowersurface of the well is defined by a lower buffer material disposed overthe sensor pad. In an additional example of the first aspect or theabove examples, the lower buffer material has an intrinsic buffercapacity of at least 2×10¹⁷ groups/m², such as an intrinsic buffercapacity of at least 4×10¹⁷ groups/m², at least 1×10¹⁸ groups/m², or atleast 2×10¹⁸ groups/m². In another example of the first aspect or theabove examples, the lower buffer material has an intrinsic buffercapacity of not greater than 1×10²¹ groups/m². In a further example ofthe first aspect or the above examples, the upper buffer material andthe lower buffer material are the same.

In an additional example of the first aspect, the upper buffer materialincludes an inorganic material.

In another example of the first aspect or the above examples, the upperbuffer material includes a ceramic material. In a particular example,the ceramic material includes an oxide of aluminum, hafnium, tantalum,zirconium, or a combination thereof. For example, the ceramic materialincludes an oxide of tantalum. In another example, the ceramic materialincludes an oxide of aluminum.

In a further example of the first aspect or the above examples, the wallmaterial includes an inorganic material. For example, the inorganicmaterial includes a ceramic material. In an example, the ceramicmaterial includes a nitride of silica or titanium. In another example,the ceramic material includes an oxide of silicon. In a further aspect,the inorganic material includes a metal material. For example, the metalmaterial includes aluminum, copper, nickel, titanium, gold, silver,platinum, or a combination thereof. In a particular example, the metalmaterial includes copper.

In an additional example of the first aspect or the above examples, thewall material includes an organic material. For example, the organicmaterial includes a polymeric material. In an example, the polymericmaterial includes poly(xylylene).

In another example of the first aspect or the above examples, the sensorand wall structure are integral to an electronic component. For example,the electronic component is disposed in cooperation with a flow chamberto place the sensor and the well wall structure in fluid communicationwith an aqueous solution. In another example, the electronic componentis in signal communication with a processor.

In a second aspect, a method of forming a sensor system includes forminga structural layer over a sensor device. The sensor device includes asensor pad. The structural layer includes a structural material havingan intrinsic buffer capacity of not greater than 1.7×10¹⁷ groups/m². Themethod further includes forming a buffer layer over the structurallayer. The buffer layer includes a buffer material having an intrinsicbuffer capacity of at least 2×10¹⁷ groups/m². The method also includesetching the buffer layer and the structural layer to define a welloperatively connected to the sensor pad.

In an example of the second aspect, the structural material has anintrinsic buffer capacity of not greater than 1×10¹⁷ groups/m². Forexample, the buffer material has an intrinsic buffer capacity of atleast 4×10¹⁷ groups/m².

In another example of the second aspect or the above examples, themethod further includes forming a passivation layer over the sensor padprior to forming the structural layer, the passivation layer disposedbetween the sensor device and the structural layer. In a furtherexample, the method further includes forming an etch stop layer over thepassivation layer. The etch stop layer is disposed between thestructural layer and the passivation layer. For example, etching caninclude exposing the passivation layer.

In an additional example of the second aspect or the above examples,forming the structural layer includes forming a first dielectric layerand forming a second dielectric layer, a material of the firstdielectric layer being different from a material of the seconddielectric layer. For example, the method can further include forming athird dielectric layer over the second dielectric layer, a material ofthe second dielectric layer being different from a material of the thirddielectric layer. In particular, the first dielectric layer can includean oxide of silicon. In another example, the second dielectric layer caninclude silicon nitride. In a further example of the second aspect orthe above examples, forming the structural layer includes depositingTEOS.

In a third aspect, a method of sequencing a polynucleotide includesapplying a particle comprising a plurality of copies of a polynucleotideto a well of a system of the first aspect, exposing the particle to anaqueous solution including a nucleotide, and measuring a response of thedevice to the exposing.

In a fourth aspect, a system includes a sensor device including a sensorpad and a well wall structure defining a well in operative connectionwith the sensor pad. A lower surface of the well is defined over thesensor pad. The well wall structure has an upper surface and a wallsurface extending between the upper surface and the lower surface. Thesystem includes a passivation film disposed over the upper surface, thewall surface and the lower surface and an isolation film disposed overthe passivation film opposite the well wall structure and extendingsubstantially parallel to and at least along a portion of the wallsurface. The passivation layer is exposed at least along a portion ofthe upper surface and at least along a portion of the lower surface.

In an example of the fourth aspect, the passivation layer includes abuffer material having an intrinsic buffer capacity of at least 2×10¹⁷groups/m². In another example of the fourth aspect or the aboveexamples, the buffer material includes an oxide of zirconium, aluminum,tantalum, hafnium, or a combination thereof. In an additional example ofthe fourth aspect or the above examples, the buffer material includes anoxide of tantalum.

In another example of the fourth aspect or the above examples, theisolation layer includes a low buffer material having an intrinsicbuffer capacity of not greater than 1.7×10¹⁷ groups/m². In an additionalexample of the fourth aspect or the above examples, the low buffermaterial includes a ceramic material. For example, the low buffermaterial includes an oxide of silicon. In an example, the low buffermaterial includes a nitride of silicon, titanium, or a combinationthereof. In an additional example of the fourth aspect or the aboveexamples, the low buffer material includes a polymeric material. Forexample, the polymeric material include poly(xylylene).

In a fifth aspect, a method of forming a sensor system includes forminga structural layer over a sensor device, the sensor device including asensor pad and etching the structural layer to define a well operativelyconnected to the sensor pad. A lower surface of the well is defined overthe sensor pad. The structurally layer has an upper surface and a wallsurface extending between the upper surface and the lower surface. Themethod includes forming a passivation film over the structural layer.The passivation film extends along at least a portion of the uppersurface and extends over the wall surface and the lower surface. Themethod further includes forming an isolation film over the passivationfilm and etching the isolation film to expose the passivation film alongat least the portion of the upper surface and at least a portion of thelower surface.

In an example of the fifth aspect, forming the structural layer includesforming a first dielectric layer and forming a second dielectric layer,a material of the first dielectric layer being different from a materialof the second dielectric layer.

In another example of the fifth aspect or the above examples, the methodfurther includes forming a third dielectric layer over the seconddielectric layer, a material of the second dielectric layer beingdifferent from a material of the third dielectric layer.

In an additional example of the fifth aspect or the above examples, thefirst dielectric layer includes an oxide of silicon. In another example,the second dielectric layer includes silicon nitride.

In a further example of the fifth aspect or the above examples, formingthe structural layer includes depositing TEOS.

In an example of the fifth aspect or the above examples, forming thepassivation layer includes depositing a buffer material having anintrinsic buffer capacity of at least 2×10¹⁷ groups/m².

In another example of the fifth aspect or the above examples, formingthe passivation layer includes depositing an oxide of aluminum,zirconium, hafnium, tantalum, or a combination thereof.

In an additional example of the fifth aspect or the above examples,forming the isolation layer includes depositing an inorganic material.In an example, the inorganic material includes a nitride of titanium,silicon, or a combination thereof.

In a further example of the fifth aspect or the above examples, formingthe isolation layer includes depositing a polymeric material. In anexample, the polymeric material includes a poly(xylylene).

In another example of the fifth aspect or the above examples, etchingthe isolation material includes anisotropic etching the isolationmaterial.

In a sixth aspect, a method of sequencing a polynucleotide includesapplying a particle comprising a plurality of copies of a polynucleotideto a well of a system of the fourth aspect, exposing the particle to anaqueous solution including a nucleotide, and measuring a response of thedevice to the exposing.

In a seventh aspect, a system includes a sensor device including asensor pad and a well wall structure defining a well in operativeconnection with the sensor pad. A lower surface of the well is definedover the sensor pad. The well wall structure has an upper surface, and awall surface extends between the upper surface and the lower surface. Ametal layer is disposed over the well wall structure and extends alongthe upper surface and the wall surface.

In an example of the seventh aspect, the metal layer includes aluminum,copper, nickel, gold, silver, titanium, platinum, or a combinationthereof. For example, the metal layer can include copper. In a furtherexample, the lower surface is free of the metal layer.

In another example of the seventh aspect or the above examples, the wallsurface extends substantially vertically.

In a further example of the seventh aspect or the above examples, thewell wall structure includes an inorganic material. In another example,the inorganic material includes a ceramic material. For example, theceramic material includes a nitride of silica or titanium. In anotherexample, the ceramic material includes an oxide of silicon.

In an eighth aspect, a method of forming a sensor system includesforming a structural layer over a sensor device, the sensor deviceincluding a sensor pad, and etching the structural layer to form atrench defining a well post over the sensor pad and a well wallstructure opposite the first structure, the well post extendingvertically higher than the well wall structure. The method furtherincludes depositing a metal layer into the trench and over the well postand the well wall structure, exposing the well post, and etching toremove the well post.

In a ninth aspect, a method of forming a sensor system includes forminga structural layer over a sensor device, the sensor device including asensor pad, etching the structural layer to form a well post over thesensor pad, depositing a metal layer to surround the well post, andetching to remove the well post.

In a tenth aspect, a method of sequencing a polynucleotide includesapplying a particle comprising a plurality of copies of a polynucleotideto a well of a system of the seventh aspect, exposing the particle to anaqueous solution including a nucleotide, and measuring a response of thedevice to the exposing.

As used herein, the terms “over” or “overlie” refers to a position awayfrom a surface relative to a normal direction from the surface. Theterms “over” or “overlie” are intended to permit intervening layers ordirect contact with an underlying layer. As described above, layers thatare disposed over or overlie another layer can be in direct contact withthe identified layer or can include intervening layers.

Note that not all of the activities described above in the generaldescription or the examples are required, that a portion of a specificactivity may not be required, and that one or more further activitiesmay be performed in addition to those described. Still further, theorder in which activities are listed are not necessarily the order inwhich they are performed.

In the foregoing specification, the concepts have been described withreference to specific embodiments. However, one of ordinary skill in theart appreciates that various modifications and changes can be madewithout departing from the scope of the invention as set forth in theclaims below. Accordingly, the specification and FIG.s are to beregarded in an illustrative rather than a restrictive sense, and allsuch modifications are intended to be included within the scope ofinvention.

As used herein, the terms “comprises,” “comprising,” “includes,”“including,” “has,” “having” or any other variation thereof, areintended to cover a non-exclusive inclusion. For example, a process,method, article, or apparatus that comprises a list of features is notnecessarily limited only to those features but may include otherfeatures not expressly listed or inherent to such process, method,article, or apparatus. Further, unless expressly stated to the contrary,“or” refers to an inclusive-or and not to an exclusive-or. For example,a condition A or B is satisfied by any one of the following: A is true(or present) and B is false (or not present), A is false (or notpresent) and B is true (or present), and both A and B are true (orpresent).

Also, the use of “a” or “an” are employed to describe elements andcomponents described herein. This is done merely for convenience and togive a general sense of the scope of the invention. This descriptionshould be read to include one or at least one and the singular alsoincludes the plural unless it is obvious that it is meant otherwise.

Benefits, other advantages, and solutions to problems have beendescribed above with regard to specific embodiments. However, thebenefits, advantages, solutions to problems, and any feature(s) that maycause any benefit, advantage, or solution to occur or become morepronounced are not to be construed as a critical, required, or essentialfeature of any or all the claims.

After reading the specification, skilled artisans will appreciate thatcertain features are, for clarity, described herein in the context ofseparate embodiments, may also be provided in combination in a singleembodiment. Conversely, various features that are, for brevity,described in the context of a single embodiment, may also be providedseparately or in any subcombination. Further, references to valuesstated in ranges include each and every value within that range.

What is claimed is:
 1. A system comprising: a sensor including a sensorpad; and a well wall structure defining a well operatively connected tothe sensor pad, the sensor pad associated with a lower surface of thewell, the well wall structure defining an upper surface and a wallsurface extending between the upper surface and the lower surface, theupper surface defined by an upper buffer material having an intrinsicbuffer capacity of at least 2×10¹⁷ groups/m² and not greater than 1×10²¹groups/m², the wall surface being defined by a wall material having anintrinsic buffer capacity of not greater than 1.7×10¹⁷ groups/m².
 2. Thesystem of claim 1, wherein the upper buffer material has an intrinsicbuffer capacity of at least 4×10¹⁷ groups/m².
 3. The system of claim 1,wherein the lower surface of the well is defined by a lower buffermaterial disposed over the sensor pad.
 4. The system of claim 3, whereinthe lower buffer material has an intrinsic buffer capacity of at least2×10¹⁷ groups/m².
 5. The system of claim 3, wherein the upper buffermaterial and the lower buffer material are the same.
 6. The system ofclaim 1, wherein the upper buffer material includes an inorganicmaterial.
 7. The system of claim 1, wherein the upper buffer materialincludes a ceramic material.
 8. The system of claim 7, wherein theceramic material includes an oxide of aluminum, hafnium, tantalum,zirconium, or a combination thereof.
 9. The system of claim 1, whereinthe wall material includes an inorganic material.
 10. The system ofclaim 9, wherein the inorganic material includes a ceramic material. 11.The system of claim 10, wherein the ceramic material includes a nitrideof silica or titanium.
 12. The system of claim 10, wherein the ceramicmaterial includes an oxide of silicon.
 13. The system of claim 9,wherein the inorganic material includes a metal material.
 14. The systemof claim 1, wherein the wall material includes an organic material. 15.The system of claim 14, wherein the organic material includes apolymeric material.
 16. The system of claim 1, wherein the sensor andwall structure are integral to an electronic component.
 17. The systemof claim 16, wherein the electronic component is disposed in cooperationwith a flow chamber to place the sensor and the well wall structure influid communication with an aqueous solution.
 18. A method of forming asensor system, the method comprising: forming a structural layer over asensor device, the sensor device including a sensor pad, the structurallayer including a structural material having an intrinsic buffercapacity of not greater than 1.7×10¹⁷ groups/m²; forming a buffer layerover the structural layer, the buffer layer including a buffer materialhaving an intrinsic buffer capacity of at least 2×10¹⁷ groups/m² and notgreater than 1×10²¹ groups/m²; and etching the buffer layer and thestructural layer to define a well operatively connected to the sensorpad.
 19. The method of claim 18, wherein the structural material has anintrinsic buffer capacity of not greater than 1×10¹⁷ groups/m².
 20. Themethod of claim 18, wherein the buffer material has an intrinsic buffercapacity of at least 4×10¹⁷ groups/m².
 21. The method of claim 18,further comprising forming a passivation layer over the sensor pad priorto forming the structural layer, the passivation layer disposed betweenthe sensor device and the structural layer.
 22. The method of claim 18,wherein forming the structural layer includes forming a first dielectriclayer and forming a second dielectric layer, a material of the firstdielectric layer being different from a material of the seconddielectric layer.
 23. The method of claim 22, further comprising forminga third dielectric layer over the second dielectric layer, a material ofthe second dielectric layer being different from a material of the thirddielectric layer.
 24. A method of sequencing a polynucleotide, themethod comprising: applying a particle comprising a plurality of copiesof a polynucleotide to a well of a system comprising: a sensor includinga sensor pad; and a well wall structure defining a well operativelyconnected to the sensor pad, the sensor pad associated with a lowersurface of the well, the well wall structure defining an upper surfaceand a wall surface extending between the upper surface and the lowersurface, the upper surface defined by an upper buffer material having anintrinsic buffer capacity of at least 2×10¹⁷ groups/m² and not greaterthan 1×10²¹ groups/m², the wall surface being defined by a wall materialhaving an intrinsic buffer capacity of not greater than 1.7×10¹⁷groups/m²; exposing the particle to an aqueous solution including anucleotide; and measuring a response of the device to the exposing.